Detecting an unsecured state of a mandrel

ABSTRACT

A method for analyzing a mandrel ( 108 ) operation in an imaging device ( 100 ) includes installing the mandrel into the imaging device; securing the mandrel between a head stock ( 144 ) and a tail stock ( 104 ); attaching a first encoder ( 212 ) to the head stock and a second encoder ( 208 ) to the tail stock; rotating the mandrel; reading signals from first encoder; reading signals from second encoder; comparing the first results and the second results; and if the first results do not match with the second results stopping the imaging device.

CROSS REFERENCE TO RELATED APPLICATIONS

Reference is made to commonly-assigned copending U.S. patent application Ser. No. 13/366,403 (now U.S. Publication No. 2013/0199389), filed Feb. 6, 2012, entitled DETECTING AN UNSECURED STATE OF A MANDREL, by Olpak et al.; and U.S. patent application Ser. No. 13/279,370 (now U.S. Pat. No. 8,441,280), filed Oct. 24, 2011, entitled SAFETY COMPONENT IN A PROGRAMMABLE COMPONENTS CHAIN, by Arie Gez; the disclosures of which are incorporated herein.

FIELD OF THE INVENTION

This invention relates to a laser imaging device for flexographic sleeves installed on a detachable mandrel and more specifically to detecting an unsecured mandrel in an imaging device.

BACKGROUND OF THE INVENTION

In many types of printing, particularly flexographic printing, offset printing and screen printing, there is an advantage in using seamless sleeves as printing elements instead of plates wrapped around printing cylinders. Seamless sleeves allow printing of continuous patterns. The use of seamless sleeves allows printing presses to operate in a smoother manner. Before a sleeve can be mounted on a printing press it has to be imaged and processed, although some materials are available today which do not require processing. The printing sleeves 116 are imaged on laser imaging device 100 as is shown in FIG. 1.

Such machines have a mandrel 108 on which a printing sleeve 116 is mounted directly. The mandrel 108 is secured in the imaging device 100 at two ends by a tail stock 104 and a head stock 144. A laser imaging head 120 is adapted to travel along the longitudinal axis of the printing sleeve 116 on imaging head tracks 124, controlled by lead screw 128.

Printing sleeve 116 is loaded over the mandrel 108. The printing sleeve 116 may be a thin-walled metal or composite cylindrical tube with media applied to the outer surface. The mandrel 108 may be provided with a number of air holes 112 in its surface through which air can be forced. This air flow creates an air bearing over mandrel 108 and permits printing sleeve 116 to be floated on a cushion of air onto the mandrel 108, the air expanding printing sleeve 116 to enable easy loading and positioning. The air is supplied by air source 140 through air hose 136. Air hose 136 is fixed to air source 140 on one side and to air inlet 132 on mandrel 108 on the other side of the air hose 136. When the supply of forced air is discontinued, printing sleeve 116 contracts to form a tight fit with mandrel 108.

Mandrel 108 is heavy and rotates at high speed. It is important, therefore, that the mandrel be securely attached at both ends. Detecting whether the mandrel 108 is securely fastened to both the trail stock 104 and head stock 144 is necessary to prevent problems during normal operation of imaging device 100.

SUMMARY OF THE INVENTION

Briefly, according to one aspect of the present invention a method for analyzing a mandrel operation in an imaging device includes installing the mandrel into the imaging device; securing the mandrel between a head stock and a tail stock; attaching a first encoder to the head stock and a second encoder to the tail stock; rotating the mandrel; reading signals from first encoder; reading signals from second encoder; comparing the first results and the second results; and if the first results do not match with the second results stopping the imaging device.

The invention and its objects and advantages will become more apparent in the detailed description of the preferred embodiment presented below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic showing a prior art laser processing system with a sleeve mounted on a mandrel adaptor using air supply; and

FIG. 2 is a schematic showing the mandrel setup between the head stock and the tail stock and encoder logic to detect whether the mandrel is secured between tail and head stock.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the disclosure. However, it will be understood by those skilled in the art that the teachings of the present disclosure may be practiced without these specific details. In other instances, well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the teachings of the present disclosure.

Mandrel 108 may spin in the imaging device 100 during imaging at speeds such as 1600 revolutions per minute (RPM). Since mandrel 108 is detachable it is necessary to assure it is properly locked in position with mandrel lock 220 as shown in FIG. 2. A mandrel 108 if detached from its secure position may cause injury, or in cases where the mandrel is not perfectly positioned, imaging quality artifacts may show on the printed material. The mandrel 108 is detachable, the mandrel design includes a screw attachment connected to spindle assembly 144 (head stock) from one side and to a “stinger” 104 connected (tail stock) on the other side.

The mandrel 108 may slightly slip from its operational position especially when mandrel 108 rotates at high speeds. In this case the cruise rotation speed may be right but the mandrel 108 image tracking mechanism will lose position. The position of mandrel 108 in the imaging device 100 is detected by encoders on both sides of the mandrel. Encoder 208 is attached to the tail stock 104 and monitors the mandrel 108 revolution next to the tail stock 104. Encoder 212 is attached to head stock 144 and monitors mandrel movement next to head stock.

The rotational speed of mandrel 108 on both ends of the mandrel is measured at the head stock 144 and tail stock 104. A comparison is made between the measurements at the tail and head stocks. Whether the mandrel is perfectly secured between the two ends 104 and 144, or whether mandrel 108 is not well secured is determined by a speed differential between the encoders.

Two encoders are used in this configuration. Encoder 212 on spindle (head stock) 144, and encoder 208 on tail stock 104. The encoders will constantly measure the signals and pulses which are generated at each of the ends during mandrel 108 rotation. The results of the encoders (number of pulses per full rotation) can also determine the level and severity of abnormal position of mandrel 108 in imaging device 100.

Head stock 144 is driven by a belt 216 which is connected to drum motor 204. A third encoder, drum motor encoder 232 is attached to motor 204. A comparison between the results of encoder 232 and 212 is made during operation of the imaging device 100. The comparison may help determine whether belt 216 is properly positioned between the drum motor 204 and spindle 144 (head stock).

Analyzer 224 is configured to read results acquired by encoders 208, 212, and 232. Input data from tail stock is received by analyzer 224 via input line 236 from tail stock, input data from head stock is received via input line 240 from head stock, and input line from drum motor is received via input line 244 from the drum motor.

The analyzer 224 will process the results acquired from all encoders (208, 212, 232), each encoder is adapted to handle input data in speeds of hundred thousand pulses per minute. In one embodiment, when an abnormal situation is encountered in the operation of the mandrel 108, an alarm 260 alerts an operator. The operator makes a decision whether to stop the operation of the imaging device or to reduce the spinning speed of the mandrel. Example of abnormal operation of the mandrel may include, mandrel slippage, mandrel vibration during spinning, or the imaging device being started without an installed mandrel. In another embodiment, the process may be automated.

Slippage of the mandrel can be detected in various slippage degrees. The degree of slippage can be derived dependent on the number of encoder slots 256 in tail stock encoder 208. In the case when a hazardous state of the mandrel 108 is detected by analyzer 224, the analyzer will send instructions to motor driver 228 via output lines 248. The instruction may be to stop or reduce speed of drum motor 204. In this case motor driver 228 will send a corresponding command (to stop or reduce speed) to drum motor 204 via output lines 252.

The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention.

PARTS LIST

-   100 imaging device -   104 tail stock -   108 mandrel -   112 air holes -   116 printing sleeve -   120 imaging head -   124 imaging head tracks -   128 lead screw -   132 air inlet into mandrel -   136 air hose -   140 air source -   144 head stock (spindle) -   204 drum motor -   208 tail stock encoder -   212 head stock (drum) encoder -   216 belt -   220 mandrel lock -   224 analyzer -   228 motor driver -   232 drum motor encoder -   236 input line from tail stock encoder -   240 input line from head stock -   244 input line from drum motor encoder -   248 output line from analyzer to motor driver -   252 output line from motor driver to drum motor -   256 encoder slots -   260 alarm 

The invention claimed is:
 1. A method for analyzing a mandrel operation in an imaging device comprising: installing the mandrel into the imaging device; securing the mandrel between a head stock and a tail stock; attaching a first encoder to the head stock and a second encoder to the tail stock; rotating the mandrel; reading signals from the first encoder to form a first set of results which represent a rotational speed of the mandrel; reading signals from the second encoder to form a second set of results which represent the rotational speed of the mandrel; comparing the first set of results to the second set of results; and if the first set of results do not match the second set of results, alerting an operator of an abnormal condition. 